a wall is the line

someone created a line; some what arbitrary, and the other what strategic.
for native folks, whom the line jumped over, it was time to move south.
military factions sent to force whole tribes and villages to pack up and flee the fertile land they had learned to love.
today the line is more of a fortress than a semaphore of power.
what are the fortress builders so afraid of?
what did it feel like to draw that line the first time?
can it be fixed/